This invention relates to a method and a system for controlling fuel ignition timing in a diesel engine, and more particularly to an improved method and system for controlling fuel ignition timing in a diesel engine having an ignition timing sensor and suitable for use in an electronic control diesel engine for a motor vehicle, wherein the optimum target ignition timing is determined in accordance with the engine operating conditions including at least an engine load and an engine speed, to control the fuel ignition timing so that the optimum target ignition timing can be obtained.
In controlling the fuel injection timing to optimize the exhaust gas purifying performance and the like in a diesel engine, particularly a diesel engine for a motor vehicle, it is necessary to obtain the optimum target fuel ignition timing in accordance with the engine operating conditions including at least an engine load and an engine speed.
Japanese Patent Applications (Laid-Open) Nos. 146023/1981 and 25584/1983 disclose methods of directly determining the target fuel ignition timing from raw data of the engine load (fuel injection quantity) and the engine speed. Furthermore, U.S. Pat. No. 4,463,729 discloses a method of controlling fuel injection timing by use of an ignition timing sensor. However, the above references teach use of the actual engine speed. When the ignition timing control must be carried out at a position where the engine speed is apparently shifted by an idle rotation speed control or the like, such control as described above cannot be carried out. Furthermore, when the fuel injection quantity is used as the engine load, it is necessary to know the fuel injection quantity; if the fuel injection quantity is mechanically controlled and the fuel ignition timing is electronically controlled, there exists the disadvantage that the fuel injection quantity must be detected by some method.